Yeah, with cantis, the swap from 27" to 700c is "can of worms" scenario. It can be done, but you need to have the right brakes to do it (probably not the ones you have now).
If you want to build your own wheels, there's no reason you can't do that on 27" rims and avoid having to redo the brakes.
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● 1971 Grandis SL ● 1972 Lambert Grand Prix frankenbike ● 1972 Raleigh Super Course fixie ● 1973 Nishiki Semi-Pro ● 1979 Motobecane Grand Jubile ●1980 Apollo "Legnano" ● 1984 Peugeot Vagabond ● 1985 Shogun Prairie Breaker ● 1986 Merckx Super Corsa ● 1987 Schwinn Tempo ● 1988 Schwinn Voyageur ● 1989 Bottechia Team ADR replica ● 1990 Cannondale ST600 ● 1993 Technium RT600 ● 1996 Kona Lava Dome ●